2.79 Noob question: copying and creating materials in Cycles
It seems that when typing the name it is referencing the previous same image with new name (not referencing external image).
So to refer external image you have to press open image and select the image.
Actually it very simple, Because blender had thumbnails display function, search filter function and many filters to show only specific formats and also options to show sub directory levels. So play with them they can be useful in many occasions.

All refereed images ( or old materials) can be selected (by browse button in left side ) till you close blender file. After closing blender file, Blender flushes all unused images (/unused materials have zero before name) and keep references to only used images(/materials). If you want to refer unused images later press fake user button. This is ubiquitous concept in all, like materials, particle systems, world materials, where ever you can browse.

You can also pack image ( image is saved with-in .blend file, it facilitates to use file in other than your system). Thus material is renderable even if original image destination is changed. But it increases blend file size and it is redundant (copies of same image). I hope these is help full for beginners.